Preparing a suitable extended abstract is not easy.
In Advice to Authors of Extended Abstracts,
SIGPLAN Notices
26, 6 (June 1991), 353-6,
!$
William Pugh provides useful advice on how to prepare a
successful extended abstract.
A PostScript
version of this paper is also available.

More entertaining advice on writing extended
abstracts, is provided by Mary-Claire van Leunen and Richard Lipton in
How to Have Your Abstract Rejected,
SIGACT News 8, 3 (July-Sep. 1976), 21-4.